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Discussion Starter #1 (Edited)
Could use some help re-setting pinion depth on an unknown rear combo that I’m putting together. I’ve got a P case along with a posi and some nice looking GM 3:70 gears. I didn’t do any measurements before pulling apart unfortunately. I’m starting with a .030 shim behind the pinion. I scored a sweet T&D pinion setting tool on a deal. It’s like a $500 kit. Anyone use one and have some advice for me? Unfortunately, I don’t have the required depth only that the gears say GM and have a part number on them. I’ll try to upload some pics this evening to this post to give some context as well.

Appreciate any help you guys can provide. Would like to be able to setup this and future rears on my own.



 

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Also, if you have a copy of the shop manual there is a step by step procedure outlined therein. By watching the video and reading the manual you will get a good grasp on the procedures and the tools and fixtures involved.
 

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Unfortunately most OEM gearsets don't have the desired pinion depth marked, so measuring it doesn't help you set it correctly or quickly. It would only serve as something you could measure afterward as a historical reference. And that would be of value only if putting that particular pinion in a different housing.
 

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Suggest scoring some pinion set up bearings, adjust shim thickness for the desired tooth contact pattern.
 

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make sure the pinion shim kit has shims less than 0.010". That was the thinnest in the kit that I bought and I had to get some more.
 

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Discussion Starter #7
Unfortunately most OEM gearsets don't have the desired pinion depth marked, so measuring it doesn't help you set it correctly or quickly. It would only serve as something you could measure afterward as a historical reference. And that would be of value only if putting that particular pinion in a different housing.
Ok this is what I ran into. In reading through the T&D tool info, they have a method for determining the correct number based on a factory housing dimension and the pinion head thickness. I'll have to see if I can get that dimension with the pinion bearing installed. What are the chances of removing and re-using the pinion bearing if I need to change the shim? I have a splitter kit and a press.

I only paid $125 for the $500 kit so I'm not really worried if it doesn't benefit this build. I plan on building a 9" for the car in the next couple seasons.
 

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The set up bearings aren't cheap think I paid close to $100 for the 12 bolt set up rear pinion bearing but well worth it if you know you are going to be doing a set up on that particular rear axle more than once. If you have the original pinion shim that was in the housing that is a great starting point especially when using OEM gear sets. Not so much with aftermarket gear sets.Think it's about a 50/50 chance of not destroying the bearing pressing it off using a splitter. There is a tool that works very well removing pressed on pinion & side carrier bearings & not scrapping them but its around $500 so not really a option unless your doing rear axles frequently.
 

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I was able to remove the bearing without damaging it. I started out with a 0.006 shim plus the original 0.025 because that was the thinnest one I had. I used a slender chisel to separate the bearing from the shoulder it was pressed against and got the bearing to move out about 1/4". After that I used a pin punch to move the bearing until it cleared the larger portion of the shaft. After it moved about an inch it dropped off freely as the shaft diameter is less once you clear the bearing seat area. Be sure you are working against the inner race, not the retainer cage. I've see photos of this being done with a gear puller but the only surface available initially to pull on is the retainer. I suppose that you could use the puller after you use the chisel to move the bearing off of the shoulder, but I didn't have a puller with arms that long so I used a pin punch and knocked the bearing off. The pin punch fit between the teeth of the gear. This is something that you will see once you get into it.
 

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As you will see in the video, it is a good idea to leave the crush sleeve out until you know you have the shims right. It seems like a pain to have to break everything back down and add the crush sleeve but if you start off with the crush sleeve in your first setup and have to change anything you will have to discard the crush sleeve and buy a new one since they can't be crushed but once.
 

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Using your instrument you can do the final assembly with the crush washers in place, (As long as it is within the range of that part) Then torque to height using your instrument to confirm. Final checks using plasti-guage and machinists dye.
 

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it is a good idea to leave the crush sleeve out until
We use the shim pack style sleeve. It's reusable.
AIRC, the last 1 came from Randy's R&P.
I think most versions of this part are available @ Summit.
 

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Discussion Starter #13
We use the shim pack style sleeve. It's reusable.
AIRC, the last 1 came from Randy's R&P.
I think most versions of this part are available @ Summit.
Does that eliminate the bs trying to get 200-300lbs of torque on the nut to compress the sleeve? If so, I'm all over that.
 

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Its easy to fab a tool to hold the rectangular companion flange for pinion nut removal / installation. Score some rectangular tube I used 1x2x11ga.
Cut one leg about 36" long then cut 3 pieces to make a box that the companion flange will fit into & weld the 3 sides of the box to one end of the 36" piece. I made the box interior about 1/2" longer & wider than Chevy it fits other makes.
Round companion flanges will require a different tool design.
 

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An ol buddy of mine who worked a Chevy dealership in 60s and ran his own shop until he passed always used .028 to start with if no other information was available.He build 100s of diffs in his time and was know to be a local expert.
 

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Discussion Starter #16
An ol buddy of mine who worked a Chevy dealership in 60s and ran his own shop until he passed always used .028 to start with if no other information was available.He build 100s of diffs in his time and was know to be a local expert.
Nice, I installed a .030 shim to start so hopefully I'm pretty close. I'm hoping to drop the carrier back in later and see how the pattern looks. I torqued down the pinion nut to about 5in-lbs (rotational) using the old crush sleeve. Guess I could have left that out to make my life easier. Will post back on how the pattern looks.
 

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Nice, I installed a .030 shim to start so hopefully I'm pretty close. I'm hoping to drop the carrier back in later and see how the pattern looks. I torqued down the pinion nut to about 5in-lbs (rotational) using the old crush sleeve. Guess I could have left that out to make my life easier. Will post back on how the pattern looks.
I have heard the .030 stated by another buddie known as Mr. 12 Bolt.
 

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The shop manual suggests starting out by adding an 0.003 to the factory 0.025 which would agree with the 0.028 suggested above. I used the original 0.025 and an 0.006 since that was what I had. It worked out pretty well. I think (which means that I'm not sure) that the manual info applies to new gears. My gears had well over 100,000 miles on them. I ended up with 0.012 backlash and a halfway decent pattern. To improve my pattern would have required more backlash. I think that meant that I needed more shims, but I decided to go with what I had given the age and wear of the gears. I won't know if I make the right choice until I have the car running which could be a year or more out.
 

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Does that eliminate the bs trying to get 200-300lbs of torque on the nut to compress the sleeve? If so, I'm all over that.
Yes.
 
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